1. Field of the Invention
This invention relates to an aqueous dispersion of elemental sulfur which has a reduced corrosive activity toward ferrous metal. More particularly, it relates to an aqueous sulfur dispersion which contains ammonia and at least one metal compound selected from the group consisting of soluble zinc and magnesium compounds dissolved in the aqueous phase.
2. Description of the Prior Art
Plants require a variety of materials for adequate nutrition. The principal materials are carbon dioxide and water, which provide the elements of carbon, hydrogen and oxygen, and which are usually available in adequate amounts from both soil and atmosphere. The supply of carbon dioxide and water is continually replenished by natural phenomena. All the other essential nutrients are normally available from the soil, but they are not replenished by nature after the plant takes them up into its foliage and fruit. When the plant is removed from the soil for consumption, in contrast to the natural cycle of return to the soil, the soil nutrient supply is reduced, and the application of fertilizer becomes necessary in time.
Thirteen elements, which are normally drawn from the soil, are currently known to be essential to plant nutrition. These elements consist of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, copper, zinc, boron, molybdenum and chlorine. Of these thirteen elements, nitrogen, phosphorus and potassium are needed by plants in relatively large quantities and are therefore called macronutrients. Calcium, magnesium, and sulfur are generally required in lesser but still substantial amounts and are classified as secondary nutrients. The remaining members of the group are known as micronutrients since they are required in very small amounts for plant growth.
Plants obtain sulfur from both the soil and the air. In the soil, sulfur is ordinarily present either in the form of sulfur containing inorganic minerals or as organic sulfur compounds in the soil organic matter or humus. In the air, sulfur is primarily present in the form of sulfur dioxide which can be directly absorbed by the leaves of plants. In addition, sulfur dioxide from the air is also carried into the soil by rain water where it may be absorbed by plants.
The discharge of sulfur oxides into the air by some large industrial centers is sufficiently large to ensure that a sulfur deficiency does not develop in nearby agricultural land. This, however, is not the case for agricultural land which is remote from such sources of atmospheric sulfur oxides. In view of limitations on the natural supply of sulfur from both air and soil, a sulfur deficiency is not uncommon in agricultural soils. Such a deficiency frequently occurs in well-leached soils containing little organic matter which are located in areas far from sources of sulfur dioxide atmospheric pollution. Crops which appear to be particularly sensitive to a sulfur deficiency include corn, sugar cane, wheat, sugar beets, and legumes such as alfalfa and peanuts.
One of the most satisfactory sources of sulfur for fertilizer purposes is elemental sulfur. Although elemental sulfur cannot be directly utilized by plants, it is slowly oxidized by microorganisms in the soil to sulfate which can be metabolized by plants. In view of the water insolubility of elemental sulfur, it serves as a highly effective slow release source of sulfur for plant nutrition which is not susceptible to leaching by rain water or irrigation. In addition to its suitability as a fertilizer, elemental sulfur is also an excellent fungicide and is widely used in agriculture for this purpose.
Elemental sulfur can be applied either to soil or plants as a dry solid. It is frequently preferable, however, to apply elemental sulfur in the form of an aqueous dispersion since a dispersion avoids the hazards associated with dust formation. In addition, an aqueous sulfur dispersion can be applied with conventional spray equipment and can be diluted to any desired concentration with water. Further, an aqueous sulfur dispersion can be readily blended with other liquid fertilizers. The preparation of a conventional aqueous sulfur dispersion is set forth in U.S. Pat. No. 2,348,736.
The use of aqueous dispersions of elemental sulfur has been hampered, however, as a consequence of their highly corrosive action with respect to ferrous metal, such as carbon steel. In the past, the use of these dispersions has required the use of storage and application equipment which is constructed of stainless steel, high chromium steel, or certain plastics.
U.S. Pat. Nos. 3,854,923; 3,909,229; and 3,997,319 are directed to a micronutrient composition consisting of a solution in anhydrous or aqueous ammonia of a zinc alkanoate which contains from 1 to 6 carbon atoms. These patents teach that the zinc salts of low molecular weight alkanoic acids are desirable sources of zinc for use in combination with ammonia as a consequence of their relatively high solubility in aqueous or anhydrous ammonia. These patents do not, however, suggest, for any purpose, the combination of an aqueous dispersion of elemental sulfur with a solution in aqueous ammonia of at least one soluble zinc and/or magnesium compound.
Similarly, U.S. Pat. No. 4,007,029 discloses the preparation and use of a liquid fertilizer composition which comprises anhydrous ammonia, at least one trace element selected from the group consisting of boron, copper, magnesium, manganese and molybdenum, and wherein a compound such as ammonium acetate, magnesium acetate or sodium acetate may be used to solubilize the trace element. This patent fails to suggest, for any purpose, the combination of an aqueous dispersion of elemental sulfur with a solution in aqueous ammonia of at least one soluble zinc and/or magnesium compound.
In addition, U.S. Pat. No. 2,957,762 discloses the use of a water-soluble stable ammine complex salt of a metal selected from Groups Ib, IIb, VIa, and VIII of the Periodic Table to inhibit the corrosive activity toward ferrous metal of aqueous ammonia solutions of ammonium salts of strong mineral acids. This patent, however, fails to suggest that any material or combination of materials could be used to reduce the corrosive activity of an aqueous dispersion of elemental sulfur.